Existing polarizing plates mostly use triacetyl cellulose films having properties such as high transmittance, optical isotropy and a zero-defect surface as a protective film for protecting a polarizing film made of polyvinyl alcohol. However, triacetyl cellulose films are vulnerable to heat and moisture, and therefore, has had a problem in that a light leakage phenomenon in which light at the edge is excessively exposed when the film is used for a long period of time in high temperature and high humidity environments due to a decrease in the degree of polarization and deterioration by moisture. In order to compensate such a disadvantage, attempts to use films with a composition having high resistance for moisture and low phase-difference properties such as cyclic olefin-based reins or acryl-based resins as a protective film for a polarizing plate have been made. Particularly, acryl-based films are known to have an advantage not only in optical properties and durability but also in costs.
However, these films have surfaces with non-polar properties, therefore, adhesive strength is not sufficiently secured when aqueous adhesives, which have been used in the art for attaching a polarizer and a protective film, are used. Methods of using non-aqueous adhesives have been proposed in order to solve such a problem. However, acryl-based films have high surface friction and have poor resistance for organic solvents, therefore, adhesive layer coating is difficult, and when adhesives including an organic solvent are used, problems such as damage on a film surface occur.
Recently, a functional coating layer such as an anti-glare layer, an anti-reflection layer and/or a hard coating layer is sometimes formed on the surface of a protective film in order to improve the physical properties of a polarizing plate and a display, however, as described above, acryl-based films have insufficient solvent resistance thereby are not smoothly attached to such a functional coating layer, and even when a coating layer is formed, a problem of the film being melted occurs, and as a result, the application has been limited.
In addition, acryl-based films generally have high surface friction, and accordingly, there are problems in that a blocking phenomenon, in which film surfaces adhere together, readily occurs when winding the film, and a slip property becomes inferior.
Accordingly, the development of an optical film satisfying durability and a slip property, and having excellent solvent resistance without inhibiting transparency has been required.